Mei symmetry and Mei conserved quantity of Appell equation for a nonholonomic system of Chetaevs type with variable mass are studied. The Appell equation and differential equation of motion of the system are set up. The expression of the total derivative of the function along the trajectory of the system with respect to t, the definition and criterion of Mei symmetry of Appell equation for a nonholonomic system of Chetaevs type with variable mass under the infinitesimal transformation of group are given. The structural equation of Mei symmetry and the expression of Mei conserved quantity expressed by Appell equation are obtained. An example is given to illustrate the application of the results.